The current official and working languages of the United Nations are

• Arabic
• Chinese
• English
• French
• Russian
• Spanish

The current languages of the United Nations are available from each body's rules of procedure:

General Assembly : Rules of Procedure, Section 8, Rules 51-57

Security Council : Provisional Rules of Procedure, Chapter 8, Rules 41-47

Economic and Social Council : Rules of Procedure, Section 7, Rules 32-35

Historical Development of United Nations Languages:

On 1 February 1946, General Assembly resolution 2 (I) established Chinese, French, English, Russian and Spanish as official languages, and English and French as working languages. 

On 24 June 1946, Security Council adopted its Provisional Rules of Procedure S/96, naming Chinese, English, French, Russian, and Spanish as official languages, and English and French as working languages.

On 7 December 1948, General Assembly resolution 247 (III)  resolved that Spanish should be a working language of the General Assembly.

On 11 December 1948, General Assembly resolution 262 (III) amended the Rules of Procedure and added Spanish as a working language. 

On 21 December 1968, General Assembly resolution 2479 (XXIII) decided to include Russian as a working language of the General Assembly and suggested the Security Council consider adding Russian and Spanish as working languages. 

On 22 January 1969, Security Council resolution 263 (1969) included Russian and Spanish as working language of the Security Council.

On 18 December 1973, General Assembly resolution 3189 (XXVIII) included Chinese as a working language of the General Assembly and suggested the Security Council consider adding Chinese as a working language.

On 18 December 1973, General Assembly resolution 3190 (XXVIII) decided to include Arabic as an official language and a working language of the General Assembly and its Main Committees.

On 17 December 1980, General Assembly resolution 35/219 A decided to include Arabic as an official and working language of the subsidiary organs of the General Assembly and requested the Security Council and Economic and Social Council also include Arabic by 1 January 1983.

On 15 April 1982, Economic and Social Council decision 1982/147, found in Resolutions and decisions of the Economic and Social Council 1st regular session of 1982, E/1982/82, page 48, included Arabic among its official languages.

On 21 December 1982, Security Council resolution 528 (1982) included Arabic as an official and working language of the Security Council.

United Nations Languages 

Arabic:

• official and working language of the General Assembly (18 Dec. 1973)
• official and working language of the subsidiary organs of the General Assembly (17 Dec. 1980)
• official language of the Economic and Social Council (15 April 1982)
• official and working language of the Security Council (21 Dec. 1982)

Chinese: 

• official language of the United Nations (except the ICJ) (1 Feb. 1946)
• official language of the Security Council (24 June 1946)
• working language of the General Assembly (18 Dec. 1973)
• working language of the Security Council (17 Jan. 1974)

English: 

• official and working language of the United Nations (except the ICJ) (1 Feb. 1946)
• official and working language of the Security Council (24 June 1946)

French: 

• official and working language of the United Nations (except the ICJ) (1 Feb. 1946)
• official and working language of the Security Council (24 June 1946)

Russian: 

• official language of the United Nations (except the ICJ) (1 Feb. 1946)
• official language of the Security Council (24 June 1946)
• working language of the General Assembly (21 Dec. 1968)
• working language of the Security Council (22 Jan. 1969)

Spanish: 

• official language of the United Nations (except the ICJ) (1 Feb. 1946)
• official language of the Security Council (24 June 1946)
• working language of the General Assembly (7 Dec. 1948)
• working language of the Security Council (22 Jan. 1969)